1. Field of the Invention
The present invention relates to color diffusion transfer photographic materials and, in greater detail, to photographic materials which are used in color diffusion transfer processes using dye developing agents.
2. Description of the Prior Art
Diffusion transfer photographic processes using dye developing agents, mainly compounds which are both a developer and a dye have been described in many patents inclusing U.S. Pat. No. 2,983,606 and British Pat. No. 804,971, etc. As is described in these patent specifications, an exposed photosensitive silver halide emulsion is developed in the presence of a dye developing agent and consequently an image-wise distribution of an unreacted unoxidized dye developing agent is formed as a function of exposure and development. The unreacted unoxidized dye developing agent is diffusible in processing solutions and thus at least a part of this image-wise distribution is transferred to a superposed image receiving element.
In a particularly preferred embodiment of these diffusion transfer processes, a photosensitive element containing a silver halide emulsion together with a dye developing agent is exposed to light and a liquid processing composition is supplied to the exposed element by, for example, dipping, applying or spraying. Before, during or after the application of the above described liquid treating composition, the exposed element is superposed on an image receiving element which can mordant the dye developing agent. In a preferred example, a photosensitive element in which a dye developing agent is included in a layer adjacent a silver halide emulsion layer so as to combine with the silver halide in the silver halide emulsion layer is superposed on an image receiving element so as to contact the emulsion layer of the photosensitive element with an image receiving layer of the image receiving element, and a liquid processing composition is supplied as a comparatively thin layer between the photosensitive element and the image receiving element. The liquid processing composition permeates into the emulsion layer and the dye developing agent layer to cause development of the developable silver halide and thus the dye developing agent is immobilized.
This immobilization depends partially upon the fact that diffusibility or solubility of the oxidation products of the dye developing agent is lower than that of the unoxidized dye developing agent. It is further believed that the immobilization depends partially upon localized decrease in alkali concentration as a function of development.
Since the unreacted dye developing agent in the non-developed area of the emulsion is diffusible, the image-wise distribution of the diffusible unoxidized dye developing agent is formed as a function of exposure and development of the silver halide emulsion. At least a part of the image-wise distribution of the diffusible unoxidized dye developing agent is transferred to the superposed image receiving layer to form a transfer image on the image receiving layer. When an element comprising a silver halide emulsion layer having a different photosensitivity is combined with a dye developing agent having a different color which is a substantially complementary color to the main sensitive range of the emulsion, namely, where an emulsion sensitive to red light is combined with a cyan dye developing agent, an emulsion sensitive to green light is combined with a magenta dye developing agent or an emulsion sensitive to blue light is combined with a yellow dye developing agent, each dye developing agent is oxidized in the exposed area of the combined emulsion and immobilized therein when each photosensitive element is treated with the liquid processing composition. Thus the residual dye developing agent in the nonexposed area is transferred to the image receiving material by diffusion.
Accordingly, where a large amount of the unoxidized dye developing agent is present in the sufficiently exposed negative area corresponding to a highlight part of an object to be photographed, the unoxidized dye developing agent diffuses into the image receiving material similar to the unoxidized dye developing agent present in the non-exposed area corresponding to a dark part of the object to be photographed, whereby a low contrast transfer image having a high maximum density is formed.
On the other hand, the dye developing agents described in U.S. Pat. Nos. 3,225,001; 2,992,106; 3,297,441; 3,134,762; 3,236,643; 3,134,673; 3,236,645; 3,134,764; 3,134,672; 3,134,765; 3,183,089; 3,135,734; 3,135,604; 3,173,906; 3,222,169; 3,183,090; 3,201,384; 3,246,985; 3,208,991; 3,142,565; 3,218,312; 3,230,086; 3,262,924; 3,275,617; 3,077,402; 3,282,913; 3,141,772; 3,299,041; 3,309,199; 2,983,605; 3,047,386; 3,076,820; 3,173,929; 3,230,083; 3,236,864; 3,239,339; 3,252,969; 3,253,001; 3,288,778; 3,209,016; 3,135,606; 3,076,808; 3,126,280; 3,236,865; 3,135,605; 3,255,205; 3,131,061; 3,347,673; 3,347,672; 3,246,016; 3,245,790; 3,086,005; 3,295,973; 3,307,847; 3,230,082 and 3,230,085, for example, 1,4-bis-(.alpha.-methyl-.beta.-hydroquinonylpropylamino)-5,8-dihydroxyanth raquinone as the cyan dye developing agent, 4-propoxy-2-(p-(.beta.-hydroquinonylethyl)phenylazo)-1-naphthol as the magenta dye developing agent and 1-phenyl-3-N-n-hexylcarboxamido-4-(p-2',5'-dihydroxyphenethyl)phenylazo)-5 -pyrazolone as the yellow dye developing agent are weak developing agents for silver halide, even if they are used in a comparatively strongly alkaline range as high as a pH of 13. Accordingly, when these dye developing agents are used, the desired maximum density, gradation and sensitivity can not be obtained. Since the immobilization of the dye developing agents is a function of the development of the emulsion, the resulting transfer image obtained by this process has an undesirable high minimum density at the highlight area, an undesirable low maximum density and a low contrast. It is believed that these are partially due to the weak development activity for silver halide of the dye developing agents and the lack of efficient use of all of the dye developing agent around the silver halide particles.
Further, in a multi-color system, emulsion layers are each developed not only by a dye developing agent having a color which is a substantially complementary color to the main photosensitive range of the layers but also by other dye developing agents in other emulsion layers. For example, a part of a magenta dye developing agent in a green sensitive emulsion diffuses into a blue sensitive emulsion and a red sensitive emulsion to cause the development thereof and is immobilized therein. Consequently, the resulting transfer image is one containing a low amount of the magenta dye.
As described above, if the immobilization of the dye developing agents caused by the development of silver halide emulsions in the exposed area is insufficient, the highlight part exhibits an undesirably high minimum density reducing the image contrast. Further, the dye developing agents transferred by diffusion are immobilized by interference with other emulsion layers to cause a remarkable deterioration of the quality of the finally resulting color positive image.
Japanese Patent Publications Nos. 4839/60, 17383/60, 10240/59, and 2241/62 disclose that some improvements can be attained by accelerating the development of the silver halide using a colorless auxiliary developing agent such as 1-phenyl-3-pyrazolidone in the processing composition to accelerate the immobilization of the dye developing agents in the photosensitive element. For example, Japanese Patent Publication No. 17383/60 suggests a combination of 1-phenyl-3-pyrazolidone with other compounds having development activity and discloses that a part thereof can be added to the photosensitive element. However, the resulting images are not sufficiently satisfactory. Particularly, where these auxiliary developing agents are used for a multi-color type multi-layer photosensitive element, it is difficult to obtain satisfactory multi-color transfer images because the development does not proceed so as to immobilize the dye developing agents to the degree desired for each dye developing agent and to the degree desired for each layer.
Further, sometimes a part of the auxiliary developing agent is transferred to the image receiving element to stain the color image.
Furthermore, the emulsion becomes unstable and aggregation occurs after or during the application thereof, because the above described auxiliary developing agents are easily crystallized at normal temperatures in a supersaturated state when they are dispersed as oil drops.